package com.hoperun.utils;

import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;

public class MD5Util
{
	
	/**
	 * 默认的密码字符串组合，用来将字节转换成 16 进制表示的字符,apache校验下载的文件的正确性用的就是默认的这个组合
	 */
	protected static char hexDigits[] = { '0', '1', '2', '3', '4', '5', '6',
			'7', '8', '9', 'a', 'b', 'c', 'd', 'e', 'f' };
	
	protected static MessageDigest messagedigest = null;
	static
	{
		try
		{
			messagedigest = MessageDigest.getInstance("MD5");
		}
		catch (NoSuchAlgorithmException nsaex)
		{
			System.err.println(MD5Util.class.getName()
					+ "初始化失败，MessageDigest不支持MD5Util。");
			nsaex.printStackTrace();
		}
	}
	
	/**
	 * 生成字符串的md5校验值
	 * 
	 * @param s
	 * @return
	 */
	public static String getMD5String(String s)
	{
		return getMD5String(s.getBytes());
	}
	
	/**
	 * 判断字符串的md5校验码是否与一个已知的md5码相匹配
	 * 
	 * @param password 要校验的字符串
	 * @param md5PwdStr 已知的md5校验码
	 * @return
	 */
	public static boolean checkPassword(String password, String md5PwdStr)
	{
		String s = getMD5String(password);
		return s.equals(md5PwdStr);
	}
	
	/**
	 * 生成文件的md5校验值
	 * 
	 * @param file
	 * @return
	 * @throws IOException
	 */
	public static String getFileMD5String(File file)
		throws IOException
	{
		InputStream fis;
		fis = new FileInputStream(file);
		byte[] buffer = new byte[1024];
		int numRead = 0;
		while ((numRead = fis.read(buffer)) > 0)
		{
			messagedigest.update(buffer, 0, numRead);
		}
		fis.close();
		return bufferToHex(messagedigest.digest());
	}
	
	public static String getMD5String(byte[] bytes)
	{
		messagedigest.update(bytes);
		return bufferToHex(messagedigest.digest());
	}
	
	private static String bufferToHex(byte bytes[])
	{
		return bufferToHex(bytes, 0, bytes.length);
	}
	
	private static String bufferToHex(byte bytes[], int m, int n)
	{
		StringBuffer stringbuffer = new StringBuffer(2 * n);
		int k = m + n;
		for (int l = m; l < k; l++)
		{
			appendHexPair(bytes[l], stringbuffer);
		}
		return stringbuffer.toString();
	}
	
	private static void appendHexPair(byte bt, StringBuffer stringbuffer)
	{
		char c0 = hexDigits[(bt & 0xf0) >> 4];// 取字节中高 4 位的数字转换, >>>
											  // 为逻辑右移，将符号位一起右移,此处未发现两种符号有何不同
		char c1 = hexDigits[bt & 0xf];// 取字节中低 4 位的数字转换
		stringbuffer.append(c0);
		stringbuffer.append(c1);
	}
	
	public static void main(String[] args) {
		System.out.println(getMD5String("123456"));
	}
}
